Ubiquitin-like polypeptide conjugates to acceptor proteins in concanavalin A- and interferon gamma-stimulated T-cells.
Monoclonal non-specific suppressor factor (MNSF), a lymphokine produced by a murine T-cell hybridoma, possesses pleiotrophic non-specific suppressive functions. MNSFbeta (a subunit of MNSF) is a 14.5 kDa fusion protein consisting of a protein with 36% homology with ubiquitin and ribosomal protein S30. The ubiquitin-like segment of MNSFbeta (Ubi-L) is an 8 kDa polypeptide with MNSF-like activity. Since the amino acids critical for the ubiquitination process are conserved in Ubi-L, we examined whether Ubi-L may conjugate with intracellular proteins in a manner similar to the ubiquitin system. Rabbit polyclonal antibodies specific for Ubi-L detected the induction of Ubi-L conjugations, including 33.5 kDa and 70 kDa molecules in concanavalin A (Con A)-stimulated T-cells, but not in lipopolysaccharide-stimulated B-cells and macrophages. High-molecular-mass conjugates were consistently present in pan-T-cells. However, free Ubi-L could not be observed in all the cells tested. Con A-activated CD8+ T-cells, but not CD4+ T-cells, induced the 70 kDa Ubi-L adduct, which was recognized by an anti-MNSF monoclonal antibody. Treatment of CD8+ T-cells with interferon (IFN) gamma also caused the expression of the 70 kDa Ubi-L adduct, whereas the responses to IFNalpha and IFNbeta were nil. Antigen- and Con A- stimulated D.10 G4.1, a murine T helper clone type 2, induced the 33.5 kDa, but not the 70 kDa, adduct. These results suggest a role for Ubi-L conjugation in the regulation of T-cell activation.
Nakamura
M
M
Department of Biochemistry, Shimane Medical University, 89-1 Enya-cho, Izumo 693, Japan.
Tanigawa
Y
Y
D000818:Animals; D000906:Antibodies / Q000378:metabolism; D015496:CD4-Positive T-Lymphocytes / Q000187:drug effects / Q000378:metabolism; D018414:CD8-Positive T-Lymphocytes / Q000187:drug effects / Q000378:metabolism; D002352:Carrier Proteins / Q000276:immunology / Q000378:metabolism*; D002460:Cell Line; D003208:Concanavalin A / Q000494:pharmacology*; D003429:Cross Reactions; D005260:Female; D007371:Interferon-gamma / Q000494:pharmacology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008970:Molecular Weight; D011817:Rabbits; D025842:SUMO-1 Protein; D013491:Suppressor Factors, Immunologic / Q000378:metabolism*; D013601:T-Lymphocytes / Q000187:drug effects* / Q000378:metabolism; D014452:Ubiquitins / Q000276:immunology
D000906:Antibodies; D002352:Carrier Proteins; D025842:SUMO-1 Protein; D013491:Suppressor Factors, Immunologic; D014452:Ubiquitins; C072169:monoclonal nonspecific suppressor factor; D003208:Concanavalin A; D007371:Interferon-gamma